title: Enzymatic pH control for biomimetic deposition of calcium phosphate coatings.
abstract: The current study examines the enzymatic decomposition of urea into carbon dioxide and ammonia as a means to increase the pH during biomimetic deposition of calcium phosphate (CaP) onto implant surfaces. The kinetics of the enzymatically induced pH increase were studied by monitoring pH, calcium concentration and conductivity of the aqueous solutions as a function of time, urease concentration and initial concentrations of calcium and phosphate ions. Cryogenic transmission electron microscopy was used to study the process of homogeneous CaP precipitation in solution, whereas CaP deposition on conventional acid-etched titanium and micropatterned polystyrene (PS) surfaces was studied using scanning electron microscopy. The data presented in this study confirm that the substrate-enzyme combination urea-urease offers strong control over the rate of pH increase by varying the concentrations of precursor salts and urease. Formation of biomimetic CaP coatings was shown to proceed via formation of ionic polymeric assemblies of prenucleation complexes. The process of deposition and corresponding coating morphology was strongly dependent on the concentration of calcium, phosphate and urease. Finally, it was shown that the substrate-enzyme combination urea-urease allowed for spatial distribution of CaP crystals along the grooves of micropatterned PS surfaces at low concentrations of calcium, phosphate and urease, stressing the sensitivity of the presented method.
authors.affiliation: Department of Biomaterials, Radboud University Medical Center, Philips van Leydenlaan 25, 6525 EX Nijmegen, The Netherlands.
authors.forename: Arnold W G
authors.initials: AW
authors.lastname: Nijhuis
authors.affiliation: Department of Biomaterials, Radboud University Medical Center, Philips van Leydenlaan 25, 6525 EX Nijmegen, The Netherlands.
authors.forename: M Reza
authors.initials: MR
authors.lastname: Nejadnik
authors.affiliation: Laboratory of Materials and Interface Chemistry and Soft Matter CryoTEM Unit, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
authors.forename: Fabio
authors.initials: F
authors.lastname: Nudelman
authors.affiliation: Department of Biomaterials, Radboud University Medical Center, Philips van Leydenlaan 25, 6525 EX Nijmegen, The Netherlands.
authors.forename: X Frank
authors.initials: XF
authors.lastname: Walboomers
authors.affiliation: Department of Tumor Immunology, Nijmegen Centre for Molecular Life Sciences, Radboud University Medical Center, Geert Grooteplein 28, 6525 GA Nijmegen, The Netherlands.
authors.forename: Joost
authors.initials: J
authors.lastname: te Riet
authors.affiliation: Department of Tissue Regeneration, MIRA Institute for Biomedical Technology and Technical Medicine, Faculty of Science and Technology, University of Twente, PO Box 217, 7500AE Enschede, The Netherlands.
authors.forename: Pamela
authors.initials: P
authors.lastname: Habibovic
authors.affiliation: Department of Tissue Regeneration, MIRA Institute for Biomedical Technology and Technical Medicine, Faculty of Science and Technology, University of Twente, PO Box 217, 7500AE Enschede, The Netherlands.
authors.forename: Zeinab
authors.initials: Z
authors.lastname: Tahmasebi Birgani
authors.affiliation: Research Center for Nano-Biomaterials, Analytical and Testing Center, Sichuan University, 610064 Chengdu, People's Republic of China.
authors.forename: Yubao
authors.initials: Y
authors.lastname: Li
authors.affiliation: Laboratory of Materials and Interface Chemistry and Soft Matter CryoTEM Unit, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
authors.forename: Paul H H
authors.initials: PH
authors.lastname: Bomans
authors.affiliation: Department of Biomaterials, Radboud University Medical Center, Philips van Leydenlaan 25, 6525 EX Nijmegen, The Netherlands.
authors.forename: John A
authors.initials: JA
authors.lastname: Jansen
authors.affiliation: Laboratory of Materials and Interface Chemistry and Soft Matter CryoTEM Unit, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
authors.forename: Nico A J M
authors.initials: NA
authors.lastname: Sommerdijk
authors.affiliation: Department of Biomaterials, Radboud University Medical Center, Philips van Leydenlaan 25, 6525 EX Nijmegen, The Netherlands. Electronic address: Sander.Leeuwenburgh@radboudumc.nl.
authors.forename: Sander C G
authors.initials: SC
authors.lastname: Leeuwenburgh
mesh_terms: D040761:Biomimetic Materials / Q000737:chemistry*; D002118:Calcium / Q000032:analysis; D002130:Calcium Phosphates / Q000737:chemistry*; D020099:Coated Materials, Biocompatible / Q000737:chemistry*; D020285:Cryoelectron Microscopy; D004553:Electric Conductivity; D006863:Hydrogen-Ion Concentration; D010710:Phosphates / Q000032:analysis; D011137:Polystyrenes / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D014025:Titanium / Q000737:chemistry; D014510:Urease / Q000378:metabolism*; D014961:X-Ray Diffraction
chemical_list: D002130:Calcium Phosphates; D020099:Coated Materials, Biocompatible; D010710:Phosphates; D011137:Polystyrenes; C020243:calcium phosphate; D014025:Titanium; D014510:Urease; D002118:Calcium
keywords: Calcification; Calcium phosphate coating; Hydroxyapatite; Patterned surfaces; Pre-nucleation clusters